K3: SSB generation

[K1LI]

I would like to know how the K3 and the KX3 generate SSB. Does the DSP generate DSB which is then filtered by the IF crystal filter, or does the DSP generate SSB which is then cleaned up by the IF filter.

K1LI

[Lyle Johnson]

In the K3, the DSP generates an SSB signal at 15 kHz.

In the KX3, the DSP generates an I and Q stream which combines to create
SSB in the quadrature baseband-to-RF mixer.

73,

Lyle KK7P


> I would like to know how the K3 and the KX3 generate SSB.

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[David Woolley (E.L)]

More generally, I think you will find that all SDR radios generate SSB
by what would be called the phasing method in analogue radios, rather
than the filter method.

--
David Woolley
Owner K2 06123

On 10/05/14 17:15, Lyle Johnson wrote:
> In the K3, the DSP generates an SSB signal at 15 kHz.
>
> In the KX3, the DSP generates an I and Q stream which combines to create
> SSB in the quadrature baseband-to-RF mixer.
>
>
>> I would like to know how the K3 and the KX3 generate SSB.
>
>

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[K1LI]

Thanks for writing, Lyle.

I am curious, then, why the (K3) SSB signal is routed through a crystal filter. Is it purely a "belt and suspenders" approach to enforcing a limit on the bandwidth of the transmitted signal?

Brian K1LI

[Larry Lopez]

The 15 K Hz signal from the DSP is a SSB signal.
This is the second IF frequency (from the antenna side).

When this is mixed with the 8.230 Mhz in you
end up with the sum and difference with the 15KHz:

Namely 8.215 and 8.245 MHz.

The 8.215 MHz filter is used to remove the
unwanted 8.245 MHz component
leaving the desired first IF frequency



K1LI [via Elecraft] wrote:

Thanks for writing, Lyle.

I am curious, then, why the (K3) SSB signal is routed through a crystal filter. Is it purely a "belt and suspenders" approach to enforcing a limit on the bandwidth of the transmitted signal?

Brian K1LI

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[Larry Lopez]

The schematics show two internal crystal filters:

one on the receive path (2 poles) K3 RF Board
It's marked BW 14 kHz.  8215.0 KHz.
This has no relay to bypass it.

one on the transmit path (4 poles) KREF3 REF/2ND TX IF
It's marked 8215.0 kHz, BW=4 kHz
This has a relay to move to bypass it.

These seem to be in addition to the 5 user accessible
crystal filters.

So there seems to be large quantities of belts and suspenders.

[wayne burdick]

Hi Larry,

> The schematics show two internal crystal filters:
>
> one on the receive path (2 poles) K3 RF Board
> It's marked BW 14 kHz.  8215.0 KHz.
> This has no relay to bypass it.

This is used to further suppress the 2nd-IF image response at 8245 kHz. It has essentially no ripple and thus no negative impact on the passband.


>
> one on the transmit path (4 poles) KREF3 REF/2ND TX IF
> It's marked 8215.0 kHz, BW=4 kHz
> This has a relay to move to bypass it.

This filter lowers the low noise floor of the IF signal feeding the transmit gain stages and main IF crystal filters. We bypass it in wideband transmit modes (AM, FM, ESSB).

This supplemental filtering is needed to achieve the K3's high blocking dynamic range, rapid fall-off of phase noise, and excellent rejection of image responses.

73,
Wayne
N6KR




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